Cambridge International AS & A Level

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Cambridge International AS & A Level

CHEMISTRY9701/41

Paper 4 A Level Structured Questions

May/June 2020

2 hours

You must answer on the question paper.

You will need: Data booklet

INSTRUCTIONS Answer all questions. Use a black or dark blue pen. You may use an HB pencil for any diagrams or graphs. Write your name, centre number and candidate number in the boxes at the top of the page. Write your answer to each question in the space provided. Do not use an erasable pen or correction fluid. Do not write on any bar codes. You may use a calculator. You should show all your working, use appropriate units and use an appropriate number of significant

figures.

INFORMATION The total mark for this paper is 100. The number of marks for each question or part question is shown in brackets [ ].

IB20 06_9701_41/5RP ? UCLES 2020

This document has 20 pages. Blank pages are indicated.

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2 Answer all the questions in the spaces provided.

1 (a)An aqueous solution of cobalt(II) contains the [Co(H2O)6]2+ complex ion. (i) Define the term complex ion. .............................................................................................................................................. ........................................................................................................................................ [1] (ii)Samples of [Co(H2O)6]2+ are reacted separately with aqueous sodium hydroxide and with an excess of aqueous ammonia.

Give the following information about these reactions. the reaction of [Co(H2O)6]2+ with aqueous sodium hydroxide

colour and state of the cobalt-containing species ......................................................... ionic equation ............................................................................................................... type of reaction .............................................................................................................

the reaction of [Co(H2O)6]2+ with an excess of aqueous ammonia colour and state of the cobalt-containing species ......................................................... ionic equation ............................................................................................................... type of reaction ............................................................................................................. [6]

(b)When concentrated hydrochloric acid is added to a solution containing [Co(H2O)6]2+, a blue solution of [CoCl4]2? is formed and the following equilibrium is established.

[Co(H2O)6]2+ + 4Cl?

[CoCl4]2? + 6H2O

Use Le Chatelier's principle to suggest the expected observations when silver nitrate solution is added dropwise to the blue solution of [CoCl4]2?. Explain your answer.

.....................................................................................................................................................

.....................................................................................................................................................

............................................................................................................................................... [2]

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3 (c) The [Co(NH3)3Cl3] complex shows stereoisomerism. Complete the three-dimensional diagrams to show the two isomers of [Co(NH3)3Cl3]. Suggest the type of stereoisomerism.

Co

Co

type of stereoisomerism ............................................. [2]

(d)Compound X, C6H18N4, is a tetradentate ligand.

X

H

H2N

N H

N

NH2

(i)Suggest why one molecule of X can form four dative bonds.

..............................................................................................................................................

..............................................................................................................................................

........................................................................................................................................ [1]

(ii)C6H18N4 reacts with aqueous cobalt(II) ions, [Co(H2O)6]2+, in a 1:1 ratio to form a new complex ion.

Construct an equation for this reaction.

........................................................................................................................................ [1]

[Total: 13]

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4

2 (a) (i)Describe and explain the trend in the solubility of the Group 2 hydroxides down the group.

..............................................................................................................................................

..............................................................................................................................................

..............................................................................................................................................

..............................................................................................................................................

..............................................................................................................................................

........................................................................................................................................ [4]

Group 2 hydroxides decompose on heating to give the corresponding metal oxide and water vapour.

(ii)Suggest which of Mg(OH)2 and Sr(OH)2 will decompose at a lower temperature. Explain your answer.

..............................................................................................................................................

..............................................................................................................................................

..............................................................................................................................................

........................................................................................................................................ [2]

[Total: 6]

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5

3The overall reaction for photosynthesis is shown.

6CO2 + 6H2O C6H12O6 + 6O2 Water is oxidised in this process according to the following half-equation.

2H2O O2 + 4H+ + 4e?

half-equation 1

(a) (i)Use these equations to deduce the half-equation for the reduction of carbon dioxide in this process.

[2]

(ii)Draw a fully labelled diagram of the apparatus that should be used to measure the standard electrode potential, Eo, of O2(g) in half-equation 1 under standard conditions. Include all necessary chemicals.

[4]

(iii)For the cell drawn in (a)(ii), use the Data Booklet to calculate the electrode is positive.

and deduce which

= .............................. V

identity of the positive electrode = ..............................

[1]

[Total: 7]

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